1. Technical Field
The present invention is in the field of liquid handling, and more specifically in the field of capillary tubes for collecting and transferring a volume of liquid such as blood from one point to another for testing or the like.
2. Introduction
Capillary tubes have long been used to collect and dispense fluids. They are commonly used in medical and research fields to extract very small (micro-liter) samples of liquids to be analyzed, such as blood samples for diabetics to determine glucose levels.
The simplest type of capillary tube is a glass or plastic tube open at both ends. For use in drawing blood, the patient's finger may be pricked with a lancet, allowing blood droplets to form at the incision point, and then one end of the capillary tube is placed adjacent to the incision site whereby blood is drawn into the tube via capillary action. The sample in the tube may then be transferred to another device, for testing or analysis. The inherent rigidity of a glass tube is quite desirable for handling by the phlebotomist and glass tubes are inexpensive to manufacture. However glass tubes are brittle, thus are prone to breakage and pose a safety concern should they break during packaging, distribution, transport or while in use.
Plastic capillary tubes are also commercially available. Plastic tubes are less likely to break than a glass tube due to the inherent toughness of some plastic materials in comparison to glass. However, depending on the polymer used to make the tube, they may not be as effective as glass at drawing blood into the tube. They may require pre-treating the interior of the tube so as to be rendered “wettable”, so that the desired fluid can be drawn into the tube by capillary action. Many plastic tubes are pre-treated prior to use with an interior coating, such as an ammonium heparin coating, for this purpose, but the coating process can be labor, process and capital intensive and render the tubes less cost effective.
Thus there is an ongoing need for capillary tubes, particularly in medical applications, that can be manufactured on a cost effective basis that is competitive with glass tubes.